Rotary tablet presses are commonly known; a rotor with an as the case may be segmented die table contains bores on a partial circle, to which lower and upper punches are assigned, which are controlled in their position by means of cam elements. In a pressing station, which has at least one upper and one lower pressing roller, the pressing material filled into the die bores is pressed to a tablet with the aid of the punches (when there is spoken from a tablet above and below, this has not necessarily to be a pharmaceutical tablet, but it may be a pressed article from any arbitrary pressing material, which contains certain active ingredients or contents which develop an effect when being applied). Usually, the produced tablets have to meet certain quality standards, like weight, hardness, height and so on. It is known to take samples of the tablet production for checking them with regard to the individual criterions in external testing devices, which are arranged next to a tablet press, or even in more remote laboratories. As the measurement times per tablet are relatively long with regard to the output of a tablet press (100 tablets per second), only random samples can be examined.
The filling of the die bores or the bores of segments, respectively, takes place via a suitable filling system, a feeder shoe for instance, wherein the amount of pressing material in the die bores depends from the position of the lower punches. It is therefore known to provide a metering cam in a station in the region of the filling station, which determines the position of the lower punches, and with it the amount to be accommodated in the die bores. When the latter is to be changed, adjustment of the metering cam takes place via a suitable adjustment equipment.
The punches are pressed with a predetermined force against the pressing material in the pressing station. This force is measured. It is also known to keep the compression force at a predetermined value by comparing the measured compression force values with a desired value. When the measured compression force value (usually the maximum one) differs from the desired value, the metering cam is adjusted in order to increase or to decrease the amount which is filled in. Thus, the tablet is produced with a constant weight of mostly constant height (cylindrical height). The regulation of the compression force takes place via a suitable control circuit, which includes the control and operating computer of the tablet press. It is commonly known to operate such tablet presses with a control and operating computer.
An essential quality criterion in the production of tablets is the amount of active ingredient and/or of the amount of excipients. This is particularly valid for pharmaceutical tablets. It has to be made certain that the tablets have a constant amount of active ingredient. Even for this case, it is known to take random samples and to measure the content of active ingredient.
There are different measurement methods for measuring the content of active ingredient of tablets, like HPLC (High Performance Liquid Chromatography), NIRS (Near Infrared Spectroscopy) or LIF (Laser Induced Fluorescence Spectroscopy).
The present invention is based on the objective to provide a method for the production of tablets with the aid of a rotary tablet press, by which it is made possible to keep the amount of active ingredient of tablets automatically constant during the production, within predetermined limits, either absolutely or relatively, with respect to the tablet weight.